1. Field of the Invention
This invention relates to a polyurethane material and a molded product of polyurethanes molded by a reaction injection molding (RIM) which uses the same material.
2. Description of the Related Art
The applicant developed an invention covering a process for manufacturing a two-colored molded product of polyurethanes by RIM techniques which comprises injecting a small amount of a surface-forming polyurethane material containing a mold release agent, a coloring agent and a catalyst into a mold cavity having a reduced pressure so that it may adhere to the whole surface of the wall of the cavity and form the surface portion of a molded product. Then another polyurethane material is injected into the cavity to form its inner portion (see Japanese Patent Application Laid-open Specification No. 6-143340). This process has made it possible to eliminate the steps of applying the mold release agent and the in-mold coating material to the cavity wall before starting the molding step, and overcomes the problem of a burr formed by the in-mold coating material.
There has, however, been a problem facing the new process, since no polyurethane material that can be considered optimum has been found for use in forming the surface portion of a molded product. The applicant, therefore, further developed an invention covering a process for forming a surface portion from a non-yellowing polyurethane material containing a hexamethylene diisocyanate (HDI) trimer (see Japanese Patent Application No. 9-92930, which is not laid-opened yet). Since an HDI trimer has a ring structure, a polyurethane material using the same shows an improved wear resistance and is able to accelerate the urethane reaction by using a specific catalyst. However, since the molecular chain of the HDI trimer is not straight, there remains a problem that a polyurethane material using a generally available HDI trimer is low in breaking elongation, inferior in flexural resistance, and subject to cracks or breaking.